Improve api-routes-apollo-server-and-client-auth Example (#10358)

1. Prevent possible race conditions of cache pruning, refetching and redirects

2. Note: the original code has the following defect.

SignOut action restarts the dev server effectively resetting the memory and erasing all the "registered users" data. You have to SignUp again after SignOut. I'm not sure how
to properly fix it a.t.m

examples/api-routes-apollo-server-and-client-auth/pages/signin.js

@@ -31,15 +31,15 @@ function SignIn() {
     const passwordElement = event.currentTarget.elements.password
 
     try {
+      await client.resetStore()
       const { data } = await signIn({
         variables: {
           email: emailElement.value,
           password: passwordElement.value,
         },
       })
-      client.resetStore()
       if (data.signIn.user) {
-        router.push('/')
+        await router.push('/')
       }
     } catch (error) {
       setErrorMsg(getErrorMessage(error))

examples/api-routes-apollo-server-and-client-auth/pages/signout.js

@@ -16,12 +16,11 @@ function SignOut() {
   const [signOut] = useMutation(SignOutMutation)
 
   React.useEffect(() => {
-    if (typeof window !== 'undefined') {
-      signOut().then(() => {
-        client.resetStore()
+    signOut().then(() => {
+      client.resetStore().then(() => {
         router.push('/signin')
       })
-    }
+    })
   }, [signOut, router, client])
 
   return <p>Signing out...</p>